Question

I have a collection: [1, 2, 3, 4, 5, 6, 7, 8, 9] from which I need to generate a random number of unique elements e.g. 5, 3, 7, 9, next time: 4, 8. My function works well but sometimes throws StackOverflowError because of recursive call on a function that generates random numbers and checks if there is no duplicates already. I wonder how I can prevent this from happening.

Answer 1

You should probably do this without using recursion. A rough sketch of an algorithm that might work better:

1. Create an empty list
2. Go through the source array and add each element with 50% probability to the list
3. Convert the list to an array
4. Use Arrays.shuffle() on the array to randomly reorder the elements

That should do the job.